Sooty Mold Affects Crape Myrtle Foliage

THE PLANT DOCTOR

September 21, 1991|By Tom MacCubbin, Special to The Sentinel

QUESTION: Our crape myrtles look as if they have soot on the foliage. The plants were bright green until a few weeks ago, but now they are yellowing and dropping their leaves. How can I restore the green?

ANSWER: It's almost fall, and the leaves on crape myrtles normally yellow as the days grow shorter. But insect pests are responsible for the sooty mold. It's a black fungus that grows on plant sap and the excreta from aphids and whiteflies.

It's too late now to worry about the pests. The crape myrtle will continue to drop leaves and will be mostly twigs by late October. But next time, an oil or soap spray will help control the insects and remove some of the sooty mold. The treatment will not improve growth.

Q: Several trees planted last spring turned yellow and died during the summer. When the plants were pulled up, the roots were still in a ball and had turned brown and mushy. The area is damp. Could the wet soil have caused the problem?

A: Lots of landscape plantings drowned in the heavy summer rains. Areas that appeared well-drained last spring turned wet and soggy during the summer. Since several trees were affected and the roots had rotted, excessive water is the logical diagnosis.

When the ground appears moist, dig down to determine how much water is in the soil. If water remains in the upper few feet of ground when a hole is dug or the soil has a sour smell, the site is likely too wet for most trees.

For damp areas, choose species that won't mind the extra moisture. Bald cypress, red maples, wax myrtle and loblolly bay are good choices. Another suggestion is to raise the level of the soil in the planting area. By mounding the soil, you might be able to plant your favorite trees - even though the remaining landscape is extra damp.

Q: A blue-flowering plant is creeping into the shady areas of my landscape. I want to eliminate the growth without damaging the trees. I like the shade, but grass won't grow there. What are some shade-loving plants that would do well in this area?

A: Keep the weedy growth a little longer, and the dayflower should disappear during the winter months. The seeds blow into the landscapes and quickly become established in the turf-free areas.

In the early spring, spot kill remaining sprigs with the herbicide Roundup or similar product and fill in with a vigorous ground cover. Some suggestions for the shady spots include Asiatic jasmine, Confederate jasmine, ferns, lilyturf, or mondo grass. Use a mulch with the plantings to block out dayflower and similar weed seeds.

Q: Our lawn was treated for chinch bugs about a week ago, but the turf is still turning brown. Will I need to have the treatment repeated to control the insects?

A: Brace yourself for about another week of declining turf. Even though the insects are under control, the damage the insects inflict on a St. Augustine lawn is long-lasting. Chinch bugs appear to inject a toxin into the lawn that continues the decline for several weeks after the pests are eliminated.

Your one treatment is likely enough until spring. To be sure, check the affected area for the pests. Whenever a large number of the pinhead-size, black adults with white crossed wings are spotted, a new treatment will be needed. Populations can build up damaging levels in about six to eight weeks but seldom do.

Q: I have tried many times to grow tomatoes but at least twice a 3-inch caterpillar stripped the plant back to the main stem. Other times something ate the tomatoes as they started to ripen. What is the best pest control?

A: Keep your eye out for caterpillars. These larva stages - usually of moths - start out as small eggs laid on the foliage and slowly grow to the big hungry crawling stages.

Where possible pick the caterpillars from the plants, but if numerous, a spray may be needed. Try a biological control containing the Bacillus bacteria marketed as Dipel or Thuricide at local garden centers. The product may take several days to eliminate the pests, but it is usually effective.

If a synthetic insecticide is needed, choose from diazinon or Sevin. Follow label instructions with all pesticides and note the days that must pass between last spray and harvest.

Q: I have tried to start some herbs in egg cartons set on a screened in porch. Each time the plants germinate but grow poorly producing leggy stems. I will give it one more try if you tell me how to keep the plants compact.

A: More sun is all you need to be a success. Any plant with long weak stems is asking for additional light. Most herbs need a full sun exposure to assume a compact growth habit.

Next time sow the seeds in the egg cartons and keep them on the porch until the fist seeds start to germinate. As soon as the seedlings are spotted send them outdoors to the full sun. Do keep the soil moist as with the summer heat and high light it will dry quickly.

Gardeners trying to start seeds in windows will have a similar problem. Most seedlings need a full day of sun and even in a southern window will lean towards the light source and grow taller than normal. The best place for seedlings is outside but bring them in if a storm approaches so the sowing will not be washed away.